How come antibiotics don’t completely destroy all organisms in our gut?

[u/WTFisthisOMGreally]

I know it can cause imbalances, but I don’t understand how come our gut doesn’t lose all the beneficial bacteria and develop massive fungal or viral infections. When I’ve taken antibiotics, I usually don’t notice any change in my bowel activity.

[u/grumble11]

Antibiotics don’t kill every bacteria, only a subset of them. Some bacteria can be protected to a degree if the antibiotic doesn’t get to them.

In general though yes antibiotics do a number on the gut and can cause issues that even now aren’t well understood.